Weird disk label after using ZFS on a LUN

If you ever used ZFS on a LUN and then tried to reuse that LUN for UFS you might have noticed a “weird” disk label on it. This is known as EFI label.

Here is how it looks in format command:

partition> p  
Current partition table (original):
Total disk sectors available: 73383902 + 16384 (reserved sectors)
Part      Tag    Flag     First Sector        Size        Last Sector
0        usr    wm                34      34.99GB         73383902
1 unassigned    wm                 0          0              0
2 unassigned    wm                 0          0              0
3 unassigned    wm                 0          0              0
4 unassigned    wm                 0          0              0
5 unassigned    wm                 0          0              0
6 unassigned    wm                 0          0              0
8   reserved    wm          73383903       8.00MB         73400286

If you use straight format command there is no way to get rid of EFI label. Instead, you have to use -e option with format to get to expert features:

bash-3.00# format -e

With -e options when you label the LUN you will be asked about the type of label you want to put on the disk:

format> label  
[0] SMI Label
[1] EFI Label
Specify Label type[1]: 0  
Warning: This disk has an EFI label. Changing to SMI label will erase all
current partitions.
Continue? y
Auto configuration via format.dat[no]? yes

I suppose you could alternatively use dd command and blank out the whole disk.